Add native Windows compatibility layer

src/api_key_manager.py

@@ -38,14 +38,14 @@ class APIKeyManager:
         """Save encrypted API key to file"""
         keys = self.load()
         keys[provider] = self.encrypt_api_key(api_key)
-        with open(self.api_keys_file, 'w') as f:
+        with open(self.api_keys_file, 'w', encoding="utf-8") as f:
             json.dump(keys, f)
     
     def load(self) -> Dict[str, str]:
         """Load and decrypt API keys"""
         if not os.path.exists(self.api_keys_file):
             return {}
-        with open(self.api_keys_file, 'r') as f:
+        with open(self.api_keys_file, 'r', encoding="utf-8") as f:
             encrypted_keys = json.load(f)
         return {
             provider: self.decrypt_api_key(key)